24 hour pay rates

I have heard of a trial in chicago called alex vs chicago in a ruling on regulating what companies can pay there 24 hour shift employees.ie. 24 hour employees make less money than 12 hour or eight hour employees. however i cannot find any info around anywhere. I believe this ruling was back in 1994, if anyone has any info on this i would appreciate knowing it and where i can find more out about it. thanks